- #36
PeterDonis
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It means no subsystem has a definite state on its own, only the whole system.vanhees71 said:
Tardigrade is first multicellular organism to be quantum entangled
In summary, a tardigrade was quantum entangled with a superconducting qubit, making it the first multicellular organism to be in this state. This raises questions about the implications of entanglement for living things. Tardigrades are microscopic animals capable of surviving extreme conditions in a hibernating state. However, in this experiment, the tardigrade was "frozen" or in a hibernating state during the entanglement process. This raises questions about the role of the tardigrade in the experiment and the nature of entanglement in living organisms.
- #37
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The subsystems of course have a definite state. Given the state ##\hat{\rho}## of the whole system, it's described by the reduced statistical operator obtained from the statistical operator describing the whole system by tracing over all other subsystems. For my spin example it's
$$\hat{\rho}_1= \sum_{\sigma_{13},\sigma_{13}',\sigma_{23}} |\sigma_{13} \rangle \langle \sigma_{13},\sigma_{23}|\hat{\rho} | \sigma_{13}',\sigma_{23} \rangle \langle \sigma_{13}'|$$
and analogously for ##\hat{\rho}_2##. The sums are over the complete sets of orthornormal states (all ##\sigma_{3}##'s running over ##\pm \hbar/2##). I also used the more compact notation
$$|\sigma_{13},\sigma_{23} \rangle=|\sigma_{13} \rangle \otimes |\sigma_{23} \rangle.$$
If the whole system is in a pure state ##\hat{\rho} = |\Psi \rangle \langle \Psi|##, the two subsystems are entangled if the subsystems are not in pure states, i.e., if the reduced density operators ##\hat{\rho}_1## and ##\hat{\rho}_2## are not projection operators.
$$\hat{\rho}_1= \sum_{\sigma_{13},\sigma_{13}',\sigma_{23}} |\sigma_{13} \rangle \langle \sigma_{13},\sigma_{23}|\hat{\rho} | \sigma_{13}',\sigma_{23} \rangle \langle \sigma_{13}'|$$
and analogously for ##\hat{\rho}_2##. The sums are over the complete sets of orthornormal states (all ##\sigma_{3}##'s running over ##\pm \hbar/2##). I also used the more compact notation
$$|\sigma_{13},\sigma_{23} \rangle=|\sigma_{13} \rangle \otimes |\sigma_{23} \rangle.$$
If the whole system is in a pure state ##\hat{\rho} = |\Psi \rangle \langle \Psi|##, the two subsystems are entangled if the subsystems are not in pure states, i.e., if the reduced density operators ##\hat{\rho}_1## and ##\hat{\rho}_2## are not projection operators.
- #38
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- #39
StevieTNZ
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- #40
manyworldsBob
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And this written on the blog "Nanoscale Views" on Saturday Dec 18, 2021, though I just stumbled on it now.
By Douglas Natelson
No, a tardigrade was not meaningfully entangled with a qubit
https://nanoscale.blogspot.com/2021/12/no-tardigrade-was-not-meaningfully.htmlBy Douglas Natelson
- #41
Nugatory
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True fact: A friend of mine once announced, after wandering around the internet in search of a better answer, that "My spirit animal is a tardigrade".
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manyworldsBob
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My new profile pic. (Photograph by Eye of Science / Science Source).
- #43
MikeWhitfield
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So is the true takeaway that this is more an experimental/modeling stunt than ground-breaking science? I cannot truly follow the math so it’s probably my deficiency speaking but I’m seeing nothing truly impressive. Seems more like “We modeled a tun-state water bear as a qubit and voila, it behaved like a qubit!” Is this a gross oversimplification?StevieTNZ said:
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